Thank you David its Cornwall, part of the Great Flat Lode trail, the monument you can see in the distance is Carn Brea, the actual building is part of Wheal Francis, this place is littered with tin mines and the various buildings needed to support the tin works, not sure what this building was for but it looks pretty foreboding in its current state

I was late getting out of there one night and it had gone dark before we got back to these buildings, the place certainly has that desolate moor feel to it that would make for a good horror story and Grimpen Mire has a lovely ring to it